Cells of the innate immune system such as macrophages express specific genes that control both virus replication and virus-induced inflammation. Dysregulation of these genes has been shown to result in increased susceptibility to either viral infections or inflammatory diseases. Our laboratory is focused on genes that control specific virus-cell interactions in monocyte-lineage cells including macrophages that cause virus- induced inflammatory demyelination in the central nervous system (CNS). These studies are particularly relevant to understanding the genetic mechanisms for initiation and sustained inflammatory demyelination mediated by monocyte-lineage cells in the human demyelinating disease multiple sclerosis (MS). Of particular importance is that we have discovered a deficiency in the key anti-inflammatory gene SHP-1 in macrophages of MS patients that results in high levels of inflammatory activity in these cells similar to that seen in MS lesions. To further define the role of SHP-1 deficiency in demyelinating disease, we are studying both anti- inflammatory and anti-viral activities in monocytes of mice that are genetically deficient in SHP-1. Recently, we have shown that SHP-1-deficient mice are profoundly susceptible to virus-induced demyelinating disease compared to wild type mice following a peripheral inoculation with relatively low amounts of Theiler's murine encephalomyelitis virus (TMEV). TMEV infection appears to predominant initially in the spleen and in inflammatory monocytes in the blood prior to entry of these cells and TMEV into the CNS. These new observations have posed important questions on how peripheral virus infection of monocytes may elicit a relatively specific targeting of monocyte-mediated inflammation in the CNS white matter. Thus, the specific aims are designed to address how TMEV infects and then stimulates monocytes in the periphery to enter the CNS in large numbers and subsequently mediate inflammatory demyelination. Specific aim 1 will characterize the initial infection and spreading of TMEV within monocyte populations following peripheral inoculation. Specific aim 2 will focus on the role for the chemokine MCP-1 and its receptor CCR2 in the spreading of TMEV to monocytes in peripheral tissues and eventual movement of these infected monocytes to the CNS. Specific aim 3 will determine whether infected inflammatory monocytes that enter the white matter following peripheral TMEV inoculation differentiate into either mature macrophages or dendritic cells within demyelinating lesions and function in demyelination. Finally, we will characterize the role for SHP-1 deficiency in allowing heightened infection and persistence of TMEV in monocyte-lineage cells that may be an essential condition for development of CNS disease. Together, the research plan presents novel approaches to further elucidate the importance of SHP-1 in monocyte-lineage cells in controlling multiple key events critical for virus-induced inflammatory diseases in the CNS. PUBLIC HEALTH RELEVANCE: An essential effector cell in the human demyelinating disease, multiple sclerosis (MS), is the macrophage. Macrophages in MS white matter lesions express multiple inflammatory cytokines, toxic molecules, and phagocytic activity that cause destruction of both myelin-forming oligodendrocytes and myelin sheathes. Yet, our knowledge of macrophage biology in demyelinating disease is incomplete. We have found that a key molecule SHP-1 stringently modulates inflammatory activities of macrophages in demyelinating disease. The present project is thus focused on defining the essential role of SHP-1 in macrophage-mediated demyelinating disease.